This invention relates to methods of making magnetic heads having low profiles and narrow pole widths.
An inductive magnetic head typically comprises an inductive coil sandwiched between a first yoke layer and a second yoke layer. The two magnetic yoke layers come into direct contact with each other at one end, to form a back closure, and define a narrow transducing gap at another end. The portions of the first and second yoke layers separated by the transducing gap are respectively called the first and second pole tips of the inductive head. To write data with narrow track widths and high linear recording densities, a magnetic head with narrow pole tips needs to be provided. However, there are technical difficulties associated with building a magnetic head with narrow pole tips. A key problem confronted by head manufacturers is the difficulty in the alignment of the two pole tips.
FIG. 1 shows a prior art approach in which a magnetic head 2 is fabricated with a first pole tip 4 wider in lateral dimension than a second pole tip 6. The wider first pole tip 4 tolerates a certain degree of misalignment during the deposition of the second pole tip 6. In the magnetic head 2, the width TW of the second pole tip 6 is intended to define the track width of the magnetic head 2. However, the problem with this approach is that due to the larger width of the first pole tip 4, magnetic flux fringing beyond the width of the second pole tip 6 is experienced. The fringing flux, such as flux lines F emanating from the second pole 6 to the first pole 4 as shown in FIG. 1A, would result in registering a data track 8 with a width W having ambiguous track boundaries, which seriously limit the track-to-track separations on the recording medium 10, such as a magnetic disk.
To solve the aforementioned problems, magnetic heads with pole tips having vertically aligned sidewalls have been suggested, exemplified by the magnetic head disclosed in U.S. Pat. No. 5,285,340, Ju et al., entitled xe2x80x9cThe Thin Film Magnetic Write Head with Conformable Pole Tipsxe2x80x9d, issued Feb. 8, 1994. FIG. 2 illustrates the prior art magnetic head taught in Ju et al. The magnetic head 12 of Ju et al. includes first and second pole tips 14 and 16 xe2x80x9cstitchedxe2x80x9d onto the respective first and second yoke layers 18 and 20. The magnetic head 12 is formed by first depositing the first yoke layer 18 onto a nonmagnetic substrate 22. A photoresist layer 24 is then spun atop the first yoke layer 18. An opening with vertically aligned inner sidewalls is formed in the photoresist layer 24. The first pole tip layer 14, the gap layer 26, and second pole tip layer 16 are sequentially deposited into the photoresist opening. After selective removal of the photoresist layer 24, the second yoke layer 20 is xe2x80x9cstitchedxe2x80x9d onto the second pole tip layer 16. The magnetic head 12 of Ju et al. includes a coil layer 28 disposed on the top of the photoresist layer 24. The elevated coil layer 28 necessitates the second yoke layer 20 to be formed with large profile curvatures. The highly curved second yoke layer 20 is undesirable in several aspects in terms of fabrication and device performance.
In the processing of thin film products, the problem of step coverage always needs to be addressed. FIG. 2A illustrates the problem of step coverage which is commonly encountered in prior art thin film device fabrication. In the thin film structure 29 of FIG. 2A, a second metallic layer 30 is deposited on a first metallic layer 32 separated by an insulating layer 34. The second metallic layer 30 has to meander through a large profile curvature defined by the underlying insulating layer 34. During deposition of the second metallic layer 30, the depositing material has a tendency to migrate on the depositing surface. As a consequence, areas may be reduced in size or be devoid of deposited material, such as area 36 above the insulating layer 34 This also applies to the deposition of the insulating layer 34 above the first metallic layer 32. That is, the larger the profile curvature of the deposited layer, the higher the probability of exposing the deposited layer with areas of material weakness, such as areas 36 shown in FIG. 2A. If the areas with material deficiency occur in the second metallic layer 30, there may be an open circuit. If the area devoid of material happens in the insulating layer 34, there will be an electrical short bridging the overlying and underlying layers 30 and 32. If the second metallic layer 30 is a second yoke layer, such as the layer 20 in the magnetic head 12 shown in FIG. 2, it will be a malfunctioning head. Accordingly, in the fabrication of thin film products, excessive step coverage problems reduce final production yield and consequently increase manufacturing costs.
Moreover, the second yoke layer 20 with a high profile curvature also increases the inductance of the magnetic head 12. The reason is that the highly curved second yoke layer 20 unnecessarily lengthens the magnetic path. The longer the magnetic path, the higher would be the inductance. A magnetic head with yoke layers having high inductance is slow in response to writing current and incapable of performing high rate data transfer onto media with high areal densities.
It should also be noted that disclosed in the aforementioned U.S. Pat. No. 5,285,340 is a single layer coil 28. Modern day storage products are built with ever decreasing physical sizes and increasing storage capacities. Magnetic heads are fabricated on microscopically confined areas with limited heat dissipation capacity. To increase the sensitivity of the magnetic head without injecting excessive current into the inductive coil, the number of coil windings are accordingly increased. To maintain the small physical size for a magnetic head, the coil layers are normally stacked together. The deposition of additional coil layers would require additional profile curvature and exacerbate the problems as explained above.
U.S. Pat. No. 5,452,164, Cole et al., entitled xe2x80x9cThe Thin Film Magnetic Write Headxe2x80x9d, issued Sep. 19, 1995 discloses another magnetic head 30 as shown in FIG. 3 herein. The vertically aligned sidewalls of the first and second pole tips 32 and 34 are made possible by the process of ion milling. As with the magnetic head 12 of Cole et al. ""164, the coil layer 36 of Ju et al. ""340 is disposed above the gap layer 38. This arrangement also results in a tall stack height covered by a highly curved second yoke layer with the consequential problems as explained above.
Presently, storage products are built with smaller sizes and with higher storage capacities. There is a need to furnish these products with rapid data writing and fast data seeking time. These features place stringent requirements in the design of a magnetic head.
It is an object of the invention to provide a magnetic head capable of writing narrow data tracks with high linear recording densities.
It is another object of the invention to provide a magnetic head capable of high frequency operation.
It is yet another object of the invention to provide a magnetic head affording ease in fabrication, thereby increasing production yield with reduced manufacturing cost.
The fabrication of the novel magnetic head of this invention begins with forming a stack of layers on a substrate. The stack of layers is then etched through a common mask, resulting in the stack of layers formed on the substrate with aligned sidewalls. Thereafter, the stack of layers is covered over and around with a protective layer which is then planarized such that the stack of layers is exposed. An etching process is employed to etch the protective layer to a predetermined thickness, which is substantially thinner than the thickness of the stack of layers. An inductive coil layer is laid on the etched protective layer and covered with an overlying yoke layer which is dielectrically separated from the coil layer. The yoke layer thus formed assumes a low profile curvature due to the thin thickness of the protective layer on the substrate. As a consequence, the overall stack height of the magnetic head is reduced, thereby reducing the inductance of the overlying yoke layer and further alleviating the step coverage problem of the magnetic head during fabrication. Production costs are accordingly reduced. Furthermore, with the vertically aligned sidewalls, the side fringing flux from one pole tip to another is substantially reduced resulting in a magnetic head capable of writing data tracks with well defined boundaries during normal operations.